1. Field Of The Invention
The present invention relates to integrated circuit processing technology. More particularly, the present invention relates to integrated circuit processing technology involving thin film dielectrics and ways to protect these thin film dielectrics from damage during the manufacturing process.
2. The Prior Art
Low voltage dielectrics in integrated circuits are easily damaged in the course of the process of manufacturing the integrated circuits by voltages generated during electronic or ionic processing. Such processes include ion implantation, reactive ion etching, plasma deposition, plasma etching, and sputtering. If a charge buildup is allowed to develop a sufficient potential difference across the two conductors separated by the dielectric, to exceed the breakdown voltage of the dielectric, the dielectric may easily be damaged. Even if the voltage generated is less than the dielectric breakdown voltage, the dielectric may still be damaged by hot electrons generated by ultraviolet light or x-rays created during the semiconductor fabrication processing steps. These electrons then be swept through the dielectric at lower voltages.
Normally, dielectrics have been protected by connecting conductor overlying them to a diffusion in the substrate to discharge the voltage via the diffusion-substrate junction and thus remove any voltage which would otherwise exist across the dielectric. As dielectrics become ever thinner, this is no longer adequate to protect them. In addition, a diffusion will protect the dielectric in only one direction, i.e., the direction in which the diffusion-substrate diode is forward biased. For example, an N-type diffusion in a P-type substrate connected to a conductive member overlying a dielectric will protect the dielectric only in the negative direction but not in the positive direction.
One application in which the protection of low voltage dielectrics is particularly critical is in the area of anti-fuse applications. An anti.TM.fuse is a structure including a dielectric located between two conductors. The dielectrics may be selectively ruptured causing an ohmic connection to be formed between the two conductors. In such an application, the anti-fuse structure will usually be associated with active devices such as programming transistors, and other transistors which form other functional parts of the circuitry. Plainly, the dielectrics breakdown voltage must be engineered to be lower than the junction breakdown voltage for the active devices if the anti-fuse is to be successfully programmed. See for example, co-pending application Ser. No. 861,519, Filed May 9, 1986, assigned to the same assignee as the present invention.